1. Field of the Invention
The present invention relates to a multi-core amplification optical fiber and a multi-core optical fiber amplifier using the same.
2. Description of the Related Art
Optical transmission using a multi-core optical fiber enables further expansion of transmission capacity by using spatial multiplexing technique, and therefore further research and development are undergoing in recent years (see K. Imamura et al., “Investigation on Multi-Core Fibers with Large Aeff and Low Micro Bending Loss” OFC2010, OWK6 (2010), T. Hayashi et al., “Low-Crosstalk and Low-Loss Multi-Core Fiber Utilizing Fiber Bend” OFC2011, OWJ3 (2011), and K. Takenaga et al., “Reduction of Crosstalk by Trench-Assisted Multi-Core Fiber” OFC2011, OWJ4 (2011)). To date, transmission experiments using a multi-core optical fiber for transmission have been reported. However, mostly all of those relate to a transmission experiment in one span in which a length of 80 km of multi-core optical fiber is used.
An optical amplifier using a multi-core-type amplification optical fiber corresponding to a multi-core optical fiber for transmission is considered to be indispensable for extending transmission distance further (see Japanese Laid-open Patent Publication No. H10-125988). To date, as a multi-core Erbium-doped optical fiber amplifier (EDFA) has been reported by Abedin et al. of OFS Laboratories in U.S., research and development of the multi-core EDFA have been accelerated (K. S. Abedin et al., “Amplification and noise properties of an erbium-doped multicore fiber amplifier” Optics Express, vol. 19, pp. 16715-16721, 2011 and K. S. Abedin et al., “Cladding-pumped erbium-doped multicore fiber amplifier” Optics Express, vol. 20, pp. 20191-20200, 2012).